Magnetic sensor, production process of the magnetic sensor and magnetic array suitable for the production process

ABSTRACT

The present invention aims to provide a magnetic sensor provided with a magnetoresistive effect element capable of stably maintaining a direction of magnetization in a magnetic domain of a free layer. 
     The magnetic sensor includes a magnetoresistive effect element provided with narrow zonal portions  11   a . . .    11   a  including a pinned layer and a free layer. Disposed below both ends of the free layer are bias magnet films  11   b . . .    11   b  composed of a permanent magnet that applies to the free layer a bias magnetic field in a predetermined direction and an initializing coil  31  that is disposed in the vicinity of the free layer and applies to the free layer a magnetic field having the direction same as that of the bias magnetic field by being energized under a predetermined condition. Further, magnetizing the bias magnet films and fixing the direction of magnetization of the pinned layer are performed by a magnetic field formed by a magnet array configured such that plural permanent magnets are arranged on a lattice point of a tetragonal lattice and a polarity of a magnet pole of each permanent magnet is different from a polarity of the other adjacent magnet pole spaced by the shortest route.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 10/689,041,filed Oct. 21, 2003, now U.S. Pat. No. 7,075,395, in the name ofToshiyuki OOHASHI and Yukio WAKUI, entitled MAGNETIC SENSOR, PRODUCTIONPROCESS OF THE MAGNETIC SENSOR AND MAGNETIC ARRAY SUITABLE FOR THEPRODUCTION PROCESS.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic sensor using amagnetoresistive effect element including a pinned layer and a freelayer, a production process of the magnetic sensor and a magnet arraysuitable for the production process.

2. Description of the Related Arts

Conventionally, a magnetoresistive effect element is applied to amagnetic sensor. For instance, the magnetoresistive effect elementincludes a giant magnetoresistive effect element (GMR element) or thelike that is provided with a pinned layer having magnetization pinned(fixed) in a predetermined direction and a free layer in which thedirection of magnetization is changed according to an external magneticfield and that presents a resistance value according to a relativerelationship between the direction of magnetization in the pinned layerand the direction of magnetization in the free layer. In the magneticsensor of this type, it is required that the direction of magnetizationin each magnetic domain in the free layer in case where the externalmagnetic field is not applied to the magnetic sensor is stablymaintained in a predetermined direction (this predetermined direction isreferred to as “initial-state direction hereinafter) in order toaccurately detect a minute external magnetic field.

In general, a thin free layer is shaped into a rectangle as viewed in aplane and the long side (long axis) of the rectangular is matched to theinitial-state direction, whereby the direction in each domain in thefree layer is matched to the initial-state direction by utilizing ashape anisotropy in which the direction of magnetization is aligned inthe longitudinal direction. Further, a bias magnet film that is apermanent magnet film is disposed at both end sections of thelongitudinal direction of the free layer to apply the magnetization inthe initial-state direction to the free layer so that the direction ofmagnetization in each magnetic domain in the free layer is returned tothe initial-state direction, with a long-term stability, whenever theexternal magnetic field disappears (see. Japanese Laid open publication2002-299728 (FIGS. 42-44)).

The state of magnetization in the free layer and the bias magnet film asdescribed above will be explained with reference to FIG. 17 that is aplan view of the free layer and the bias magnet film. In FIG. 17, a freelayer 100 is formed to have a longitudinal direction in an X-axisdirection, and a pair of bias magnet films 101 and 102 are arranged atboth ends of the longitudinal direction.

At a stage of forming these films, the directions of magnetization ineach magnetic domain of the free layer 100 and the bias magnet films 101and 102 are not aligned to the initial-state direction that is thelongitudinal direction of the free layer as shown by arrows in FIG. 17A.When an external magnetic field whose magnitude is changed in adirection (Y-axis direction) perpendicular to the longitudinal directionof the free layer is applied to the magnetic sensor in which the freelayer 100 and the bias magnet films 101 and 102 are in above-mentionedstate, for measuring a resistance value of the magnetic sensor, ahysteresis occurs as shown in FIG. 18A. As apparent from this, in themagnetic sensor wherein the directions of magnetization in the freelayer 100 and the bias magnet films 101 and 102 are not aligned to thelongitudinal direction of the free layer, the resistance value for theexternal magnetic field being in the vicinity of “0” fluctuates in arange shown by an arrow in FIG. 18A, resulting in that the magneticsensor cannot accurately detect a minute magnetic field.

Subsequently, when a magnetic field having a magnitude greater than acoersive force Hc of the bias magnet films 101 and 102 is applied in thelongitudinal direction (X-axis positive direction) to the magneticsensor in which the free layer 100 and the bias magnet films 101 and 102are in a state shown in FIG. 17A in order to perform an initializationof the free layer 100 and the magnetization of the bias magnet films 101and 102, the directions of magnetization in each magnetic domain in thefree layer 100 and the bias magnet films 101 and 102 are matched to theinitial-state direction as shown in FIG. 17B.

When an external magnetic field whose magnitude is changed within arange smaller than the coersive force Hc of the bias magnet films 101and 102 in the Y-axis direction is applied to the magnetic sensor whichis in the above-mentioned state, the direction of magnetization in themagnetic domain in the free layer 100 is changed as shown in FIG. 17C,and then, after eliminating the external magnetic field, the directionof magnetization in each magnetic domain in the free layer 100 isreturned to the initial-state direction as shown in FIG. 17D like thatas shown in FIG. 17B. When the resistance value of the magnetic sensoris measured in this case, the hysteresis is decreased, so that theresistance value for the external magnetic field being in the vicinityof “0” becomes approximately constant. Accordingly, the magnetic sensorhaving the free layer 100 initialized and the bias magnet films 101 and102 magnetized can accurately detect a minute magnetic field.

However, when an external magnetic field having a magnitude smaller thanthe coersive force of the magnet films 101 and 102 but relatively greatand having a main component in the direction (X-axis negative direction)reverse to the initial-state direction is applied to the magnetic sensor(the magnetic sensor having the free layer 100 initialized and the biasmagnet films 101 and 102 magnetized), the direction of magnetization ineach magnetic domain in the free layer is changed from the state shownin FIG. 19A to the state shown in FIG. 19B, and even if the externalmagnetic field is eliminated, the direction of magnetization in eachmagnetic domain in the free layer 100 does not match (return) to theinitial-state direction. As a result, the magnetic sensor has ahysteresis again with respect to the external magnetic field, entailinga problem of deteriorating the detection accuracy of the magnetic field.

SUMMARY OF THE INVENTION

Accordingly, one of objects of the present invention is to provide amagnetic sensor capable of satisfactorily maintaining a detectionaccuracy even after a great external magnetic field is applied thereto.Further, another object of the present invention is to provide amagnetic sensor capable of efficiently magnetizing the aforesaid biasmagnet films, a production process of the magnetic sensor and a magnetarray suitable for the production process.

According to the feature of the present invention, a magnetic sensorcomprising a magnetoresistive effect element including a pinned layerand a free layer comprises a bias magnet film composed of a permanentmagnet for producing a bias magnet field for (in) the free layer in apredetermined direction and an initializing coil that is provided in thevicinity of the free layer and applies to the free layer a magneticfield in the direction same as the direction of the bias magnetic fieldby being energized under a predetermined condition.

According to the above structure, the initializing coil is energizedunder a predetermined condition to thereby generate an initializingmagnetic field for returning the direction of magnetization in eachmagnetic domain in the free layer to the direction same as the directionof the bias magnetic field by the bias magnet film, whereby thedirection of magnetization in each magnetic domain in the free layer canbe corrected even if the direction of magnetization is disturbed due tosome reason such as when a strong magnetic field is applied to themagnetic sensor. As a result, a change in the resistance value to themagnetic field does not have hysteresis, whereby a magnetic sensor canbe provided that can detect even a minute magnetic field with highprecision over a long period.

Another feature of the present invention is that a production process ofa magnetic sensor comprising, on a substrate, a pinned layer, a freelayer and a bias magnet film being a permanent magnet that applies abias magnetic field to the free layer to form a magnetoresistive effectelement having a resistance value varying according to a relative anglemade by a direction of magnetization in the pinned layer and a directionof magnetization in the free layer, comprises a step of preparing amagnet array configured such that plural permanent magnets are arrangedon a lattice point of a tetragonal lattice and a polarity of a magnetpole of each permanent magnet is different from a polarity of the otheradjacent magnet pole spaced by the shortest route (i.e., shortestdistance), a step of manufacturing a wafer, including the substrate(s),on which plural island-like element films are interspersed, each elementfilm including a film that becomes the pinned layer, a film that becomesthe free layer and a film that becomes the bias magnet film and a stepof disposing (placing, arranging) the wafer in the vicinity of themagnet array so as to establish a predetermined relative positionalrelationship between the wafer and the magnet array and magnetizing thefilm that becomes the bias magnet film of the plural element films byutilizing a magnetic field formed between one magnet pole of the magnetpoles of the magnet array and other magnet pole, of the magnet poles ofthe magnet array, that is adjacent to the one magnet pole spaced by theshortest route (from the one magnet pole).

The magnet array is configured such that plural permanent magnets arearranged at a lattice point of a tetragonal lattice and the polarity ofthe magnetic pole of each permanent magnet is different from thepolarity of the other adjacent magnetic pole spaced by the shortestroute (in the same plane), as viewed in a plane. Accordingly, thefollowing magnetic fields are formed above the magnet array as viewed ina plane of the magnet array: a magnetic filed formed from one N-pole inthe rightward direction to S-pole that is present at the right side ofthe N-pole, a magnetic field formed from the N-pole in the upwarddirection to S-pole that is present at the upper side of the N-pole, amagnetic field formed from the N-pole in the leftward direction toS-pole that is present at the left side of the N-pole and a magneticfield formed from the N-pole in the downward direction to S-pole that ispresent at the lower side of the N-pole (see FIG. 13). Similarly, thefollowing magnetic fields are formed to (toward) some S-pole: a magneticfield formed in the leftward direction from N-pole that is present atthe right side of this S-pole, a magnetic field formed in the downwarddirection from N-pole that is present at the upper side of this S-pole,a magnetic field formed in the rightward direction from N-pole that ispresent at the left side of this S-pole and a magnetic field formed inthe upward direction from N-pole that is present at the lower side ofthis S-pole.

In this process, a wafer, including the substrate(s), on which pluralisland-like element films is interspersed, each element film including afilm that becomes the pinned layer, a film that becomes the free layerand a film that becomes the bias magnet film is disposed (placed, set,or arranged) in the vicinity of the magnet array so as to establish apredetermined relative positional relationship between the wafer and themagnet array and thereby the film that becomes the bias magnet film ofthe plural element films is magnetized by utilizing the above-mentionedmagnetic field formed by the magnet array. Therefore, a magnetic sensorwherein magnetization directions of the bias magnet films are crossed(perpendicular in this case) to each other on a single substrate (amonolithic substrate) can efficiently be manufactured.

More specifically, the step of manufacturing the wafer includes a stepof forming each film, that becomes the free layer, of the plural elementfilms in such a manner as to have a shape with a long axis and a shortaxis, and in such a manner that at least one of the long axes of thefilms, that become the free layers, of the plural element films isperpendicular to the long axis of the other film, that becomes the freelayer, of the plural element films, and a step of forming the film thatbecomes the bias magnet film at both ends of each film, that becomes thefree layer, in the direction of the long axis, wherein the predeterminedrelative positional relationship in the step of magnetizing the filmthat becomes the bias magnet film is a relative relationship, betweenthe wafer and the magnet array, that matches the direction ofmagnetization of the film that becomes the bias magnet film with thedirection of the long axis of the film that becomes the free layerhaving the bias magnet film provided at both ends thereof, by a magneticfield formed by the magnet array.

Further, in this case, it is preferable to include a step of arrangingthe wafer in the vicinity of the magnet array so as to establish arelative positional relationship, between the wafer and the magnetarray, that is different from the predetermined relative positionalrelationship, whereby the direction of magnetization of the film, thatbecomes the pinned layer, of the plural element films is pinned byutilizing the magnetic field formed by the magnet array.

According to this method, the magnet array used for magnetizing the filmthat becomes the bias magnet film is also used for fixing the directionof magnetization in the pinned layer, whereby a magnetic sensor(two-axis magnetic sensor that can detect the respective magnetic fieldswhose directions are perpendicular to each other) wherein magnetizationdirections of the bias magnet films are crossed (perpendicular in thiscase) to each other on a single substrate can efficiently bemanufactured with low cost.

Moreover, the present invention provides a magnet array configured suchthat plural permanent magnets, each having an approximately rectangularparallelepiped shape in which the sectional shape perpendicular to onecentral axis of the rectangular parallelepiped is approximately square,are arranged such that the center of gravity of the edge face havingapproximately square shape is matched with a lattice point of thetetragonal lattice, and the polarity of the magnetic pole of eachpermanent magnet thus arranged is different from the polarity of themagnetic pole of the adjacent other permanent magnet spaced by theshortest route.

That is, this magnet array is the one where the plural permanent magnetsare disposed such that the center of gravity of the edge face havingapproximately square shape is matched with a lattice point of thetetragonal lattice, a side of the edge face having said approximatelysquare shape is on the same line on which a side of the other edge facedisposed in the same row, the edge faces are in a single same plane, andthe polarity of the magnetic pole of each permanent magnet thus arrangedis different from the polarity of the magnetic pole of the adjacentother permanent magnet spaced by the shortest route.

As described above, magnetizing each film that becomes the bias magnetfilm and/or fixing the direction of magnetization in the layer thatbecomes the pinned layer of the above-mentioned two-axis magnetic sensorcan efficiently be performed by using the magnet array, for example.Therefore, with the magnet array, it is possible to manufacture thetwo-axis magnetic sensor with low cost.

Further, this magnet array can be “A magnet array including pluralpermanent magnets, each having an approximately rectangularparallelepiped shape and having a sectional shape, perpendicular to onecentral axis of the rectangular parallelepiped, which is approximatelysquare, and each having poles formed at both edge faces, one of whichhas the approximately square shape perpendicular to the central axis ofthe rectangular parallelepiped; wherein

the plural permanent magnets are arranged in such a manner that eachcenter of gravity of the edge faces having the approximately squareshape is matched with a lattice point of a tetragonal lattice, a certainside of sides forming one of the edge faces of the plural permanentmagnets disposed in a certain row of the tetragonal lattice and acertain side of sides forming one of the edge faces of the other pluralpermanent magnets disposed in the same row of the tetragonal lattice isin a same straight line, all the edge faces having the square shapes ofthe permanent magnets are placed in an approximately same single plane,and any two of the polarities of the magnetic poles of the permanentmagnets disposed adjacent each other and spaced by the shortest routeare different each other.” and this array can preferably be used tomagnetize the bias magnetic films and the like of the magnetic sensormentioned above.

In addition, “A magnet array including plural permanent magnets, eachhaving an approximately rectangular parallelepiped shape and having asectional shape, perpendicular to one central axis of the rectangularparallelepiped, which is approximately square, and each having polesformed at both edge faces, one of which has the approximately squareshape perpendicular to the central axis of the rectangularparallelepiped and a thin plate-like yoke formed of a magnetic material;wherein

the plural permanent magnets are arranged in such a manner that eachcenter of gravity of the edge faces having the approximately squareshape is matched with a lattice point of a tetragonal lattice, a certainside of sides forming one of the edge faces of the plural permanentmagnets disposed in a certain row of the tetragonal lattice and acertain side of sides forming one of the edge faces of the other pluralpermanent magnets disposed in the same row of the tetragonal lattice isin a same straight line, all the edge faces having the square shapes ofthe permanent magnets are placed in an approximately same single plane,and any two of the polarities of the magnetic poles of the permanentmagnets disposed adjacent each other and spaced by the shortest routeare different each other; and

the yoke comprises plural through holes each of which has a shape whichis the approximately same as the sectional shape which is approximatelysquare and the holes being arranged at the positions where the permanentmagnets are disposed, and the yoke being arranged in such a manner thatthe same single plane in which all the edge faces of the permanentmagnets are placed is disposed between an upper surface and a lowersurface of the yoke when the permanent magnets are inserted into thethrough holes.” can preferably be used to magnetize the bias magneticfilms and the like of the magnetic sensor mentioned above.

The magnet array has the yoke formed of the magnetic material, andtherefore, it can lead magnetic flux lines from the permanent magnets todesirable portions. Accordingly, it is possible to magnetize the biasmagnetic film of the magnetic sensor and the like efficiently by themagnet array.

In this case, it is preferable that the yoke have through openingsserving as air gaps formed between the through holes that are adjacenteach other and that are spaced by a shortest route.

Since this magnet array has through openings serving air gaps betweenthe through holes that are adjacent each other and that are spaced by ashortest route (the edge faces having poles whose polarities aredifferent from (opposite) each other are inserted into those two throughholes), the magnetic flux concentrates both in the through openings andin a space close to the through openings. In other words, this magnetarray can provide a narrow space local region with a magnetic fieldwhose magnitude is great and whose direction is stably constant.Therefore, it is possible to magnetize the bias magnetic film of themagnetic sensor and the like efficiently by this magnet array.

It is also preferable that the yoke have openings at regions each ofwhich is surrounding a center of gravity of a square drawn by linesconnecting the lattice points of the tetragonal lattice in a plan view.This magnet array has not only above mentioned through openings but alsothe different openings.

The regions where the openings are formed is the region surrounding acenter of gravity of a square drawn by lines connecting the latticepoints of the tetragonal lattice. This regions is where magnetic fluxlines stemming from the poles cross (or collide) to one another and thusthe magnetic fields are unstable. Therefore, since the openings caneliminate instability of the magnetic field between poles havingdifferent polarities each other, the magnetic field can be made to bemore linear, and thus, the magnetic field is provided which is morestable and whose magnitude is greater than the magnetic field for localregions in the neighborhood of the through openings. With this reason,it is possible to magnetize the bias magnetic film of the magneticsensor and the like efficiently by this magnet array.

It is also preferable that each of the through holes of the yoke have asquare portion having a square shape which is the approximately same asthe shape of the sectional square shape of the permanent magnet in aplan view and a margin portions swelling outwardly from the square ateach of corners of the square portion. When forming the through hole, inthe yoke, having a square shape by etching, if the corner of the throughhole is not completely etched, the permanent magnet may not be insertedinto the through hole, since the corners of the thorough hole may becomearc-like shapes. However, since the margin portions are etched in themagnet array mentioned above in forming the through holes by etching,the permanent magnet can be assuredly inserted into the through hole inthe magnet array.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, aspects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a plan view of a magnetic sensor in accordance with anembodiment of the present invention;

FIG. 2 is a schematic enlarged plan view of a first X-axis GMR elementshown in FIG. 1;

FIG. 3 is a schematic sectional view of the first X-axis GMR elementshown in FIG. 2 cut by a plane along a line 1-1 in FIG. 2;

FIG. 4 is a view showing a structure of a spin valve film of the firstX-axis GMR element shown in FIG. 2;

FIG. 5 is a graph showing by a solid line a resistance change of thefirst X-axis GMR element shown in FIG. 1 for a magnetic field changed inthe X-axis direction and showing by a broken line a resistance changethereof for a magnetic field changed in the Y-axis direction;

FIG. 6A is an equivalent circuit diagram of an X-axis magnetic sensorincluded in the magnetic sensor shown in FIG. 1;

FIG. 6B is a graph showing a change of output for the magnetic fieldchanged in the X-axis direction of the X-axis magnetic sensor;

FIG. 7A is an equivalent circuit diagram of a Y-axis magnetic sensorincluded in the magnetic sensor shown in FIG. 1;

FIG. 7B is a graph showing a change of output for the magnetic fieldchanged in the Y-axis direction of the Y-axis magnetic sensor;

FIG. 8A is another equivalent circuit diagram of an X-axis magneticsensor included in the magnetic sensor shown in FIG. 1;

FIG. 8B is a graph showing a change of output for the magnetic fieldchanged in the X-axis direction of the X-axis magnetic sensor;

FIG. 9A is another equivalent circuit diagram of a Y-axis magneticsensor included in the magnetic sensor shown in FIG. 1;

FIG. 9B is a graph showing a change of output for the magnetic fieldchanged in the Y-axis direction of the Y-axis magnetic sensor;

FIG. 10 is a plan view of a quartz glass, during a process forfabricating the magnetic sensor shown in FIG. 1, having the spin valvefilm formed thereon;

FIG. 11 is a plan view showing a metal plate for preparing a magnetarray used upon fabricating the magnetic sensor shown in FIG. 1 and apermanent bar magnet inserted into the metal plate;

FIG. 12 is a sectional view of the magnet array used upon fabricatingthe magnetic sensor shown in FIG. 1;

FIG. 13 is a perspective view wherein a part of a magnet of the magnetarray shown in FIG. 12 is taken out;

FIG. 14 is a view showing one of processes for fabricating the magneticsensor shown in FIG. 1;

FIG. 15 is a conceptional view showing a method of magnetizing a biasmagnet film of each GMR element of the magnetic sensor shown in FIG. 1;

FIG. 16 is a conceptional view showing a method of pinning a directionof magnetization in the pinned layer of each GMR element of the magneticsensor shown in FIG. 1;

FIGS. 17A, 17B, 17C and 17D are plan views each showing a state ofmagnetization of the free layer and the bias magnet films of the GMRelement, wherein FIG. 17A is a view showing a state of the bias magnetfilms before they are magnetized, FIG. 17B is a view showing a state ofthe bias magnet films after they are magnetized, FIG. 17C is a viewshowing a state in which an external magnetic field is applied and FIG.17D is a view showing a state after the external magnetic field iseliminated;

FIG. 18A is a graph showing a resistance change, for the externalmagnetic field, of the GMR element in a state before the bias magnetfilms are magnetized;

FIG. 18B is a graph showing a resistance change, for the externalmagnetic field, of the GMR element in a state after the bias magnetfilms are magnetized;

FIGS. 19A, 19B and 19C are plan views each showing a state ofmagnetization of the free layer and the bias magnet films of the GMRelement, wherein FIG. 19A is a view showing a state of the bias magnetfilms before they are magnetized and that the external magnetic field isnot applied, FIG. 19B is a view showing a state in which a strongexternal magnetic field is applied and FIG. 19C is a view showing astate after the strong external magnetic field is eliminated;

FIG. 20 is a schematic enlarged plan view of a first X-axis GMR elementof a magnetic sensor according to another embodiment of the presentinvention;

FIG. 21 is a plan view of a magnetic sensor (N-type) in accordance withanother embodiment of the present invention;

FIG. 22 is a plan view of a magnetic sensor (S-type) in accordance withanother embodiment of the present invention;

FIG. 23 is a fragmentary plan view of the yoke of the magnet array MB inaccordance with the present invention;

FIG. 24 is a fragmentary enlarged plan view of the yoke shown in FIG.23;

FIG. 25 is a sectional view of the yoke shown in FIG. 24 cut by a planealong a line 2-2 in FIG. 24;

FIG. 26 is a plan view of a through hole of the yoke shown in FIG. 23;

FIG. 27 is a sectional view of a substrate for the magnet array MB inaccordance with the present invention;

FIG. 28 is a fragmentary plan view of the substrate for the array shownin FIG. 27;

FIG. 29 is a sectional view of a thin plate which will become thesubstrate for the array shown in FIG. 27;

FIG. 30 is a view showing one of processes for fabricating the magnetarray MB;

FIG. 31 is a view showing one of processes for fabricating the magnetarray MB;

FIG. 32 is a view showing one of processes for fabricating the magnetarray MB;

FIG. 33 is a view showing one of processes for fabricating the magnetarray MB;

FIG. 34 is a perspective view wherein a part of a magnet of the magnetarray MB and the yoke are taken out;

FIG. 35 is a fragmentary sectional view of the magnet array MB;

FIG. 36 is a conceptional plan view of the magnet array MB to explain amagnetic field by the magnet array MB;

FIG. 37 is a conceptional plan view of the magnet array MA to explain amagnetic field by the magnet array MA;

FIG. 38 is a conceptional view showing a method of pinning a directionof magnetization in the pinned layer of each GMR element of the magneticsensor shown in FIGS. 21 and 22;

FIG. 39 is a sectional view showing a relative positional relationshipbetween a substrate and the magnet array MB when magnetizing the biasmagnet file of each GMR element of the magnetic sensor shown in FIGS. 21and 22; and

FIG. 40 is a conceptional view showing a method of magnetizing a biasmagnet film of each GMR element of the magnetic sensor shown in FIGS. 21and 22.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of a magnetic sensor in accordance with the presentinvention will now be described with reference to the drawings. Thismagnetic sensor is classified into N-type and S-type depending upon aproduction process described later. FIG. 1 is a plan view wherein anN-type magnetic sensor 10 and an S-type magnetic sensor 50 are placedside by side. The N-type magnetic sensor 10 and the S-type magneticsensor 50 have substantially the same shape and same configurationexcept that a direction of fixed magnetization in a pinned layer shownby black-solid arrows in FIG. 1 and a direction of magnetization in aninitial state in a free layer shown by outline arrows in FIG. 1 aredifferent from each other. Accordingly, the following explanation ismainly focused on the N-type magnetic sensor 10.

The magnetic sensor 10 comprises, as shown in FIG. 1, a single chip (asingle substrate or a monolithic chip) 10 a made of a quartz glass,which has a rectangular shape (almost square shape) viewed in a planehaving sides along an X-axis direction and Y-axis directionperpendicular to each other, and has a little thickness in a Z-axisdirection perpendicular to the X-axis and Y-axis, plural insulatinglayers 10 b (wiring layers are included in this insulating layers)laminated on the substrate 10 a shown in FIG. 3, a total of eight GMRelements 11 to 14, 21 to 24 formed on the uppermost layer 10 b 1 of theinsulating layers 10 b and a total of eight initializing coils (coilsfor initializing) 31 to 34 and 41 to 44.

The first X-axis GMR element 11 is formed at a portion a little downwardfrom the almost central part in the Y-axis direction of the chip 10 aand in the vicinity of an end portion of the X-axis negative direction.The direction of pinned magnetization of the pinned layer of the GMRelement 11 is in the X-axis negative direction as shown by a black-solidarrow in FIG. 1. The second X-axis GMR element 12 is formed at a portiona little upward from the almost central part in the Y-axis direction ofthe chip 10 a and in the vicinity of the end portion of the X-axisnegative direction. The direction of pinned magnetization of the pinnedlayer of the GMR element 12 is in the X-axis negative direction shown bya black-solid arrow in FIG. 1. The third X-axis GMR element 13 is formedat a portion a little upward from the almost central part in the Y-axisdirection of the chip 10 a and in the vicinity of an end portion of theX-axis positive direction. The direction of pinned magnetization of thepinned layer of the GMR element 13 is in the X-axis positive directionas shown by a black-solid arrow in FIG. 1. The fourth X-axis GMR element14 is formed at a portion a little downward from the almost central partin the Y-axis direction of the chip 10 a and in the vicinity of the endportion of the X-axis positive direction. The direction of pinnedmagnetization of the pinned layer of the GMR element 14 is in the X-axispositive direction shown by a black-solid arrow in FIG. 1.

The first Y-axis GMR element 21 is formed at a portion a little leftwardfrom the almost central part in the X-axis direction of the chip 10 aand in the vicinity of an end portion of the Y-axis positive direction.The direction of pinned magnetization of the pinned layer of the GMRelement 21 is in the Y-axis positive direction as shown by a black-solidarrow in FIG. 1. The second Y-axis GMR element 22 is formed at a portiona little rightward from the almost central part in the X-axis directionof the chip 10 a and in the vicinity of the end portion of the Y-axispositive direction. The direction of pinned magnetization of the pinnedlayer of the GMR element 22 is in the Y-axis positive direction shown bya black-solid arrow in FIG. 1. The third Y-axis GMR element 23 is formedat a portion a little rightward from the almost central part in theX-axis direction of the chip 10 a and in the vicinity of an end portionof the Y-axis negative direction. The direction of pinned magnetizationof the pinned layer of the GMR element 23 is in the Y-axis negativedirection as shown by a black-solid arrow in FIG. 1. The fourth Y-axisGMR element 24 is formed at a portion a little leftward from the almostcentral part in the X-axis direction of the chip 10 a and in thevicinity of the end portion of the Y-axis negative direction. Thedirection of pinned magnetization of the pinned layer of the GMR element24 is in the Y-axis negative direction shown by a black-solid arrow inFIG. 1.

Each of the GMR elements 11 to 14 and 21 to 24 has substantially thesame structure except for the position on the chip 10 a. Therefore, thefirst X-axis GMR element 11 is taken as a representative examplehereinbelow for explaining the structure thereof.

The first X-axis GMR element 11 comprises, as shown in FIG. 2 that is aplan view and FIG. 3 that is a schematic sectional view of the firstX-axis GMR element 11 cut by a plane along a line of 1-1 in FIG. 2, aplurality of narrow zonal portions 11 a . . . 11 a made of a spin valvefilm SV and having a longitudinal direction in the Y-axis direction andbias magnet films (hard ferromagnetic thin film layer and become apermanent magnet film by magnetization) 11 b . . . 11 b that are made ofhard ferromagnetic materials, having high coercive force and highsquareness ratio, such as CoCrPt. Each of the narrow zonal portions 11 a. . . 11 a extends in the X-axis direction on the upper surface of eachof the bias magnet films 11 b . . . 11 b, and joins to the adjacentnarrow zonal portion 11 a to thereby form a so-called “zig-zag shape” aswell as to thereby magnetically join to each of the bias magnet films 11b . . . 11 b at the upper surface of each of the bias magnet films 11 b. . . 11 b.

As shown in FIG. 4 that illustrates the film structure, the spin valvefilm SV of the first X-axis GMR element 11 includes a free layer F, aconductive spacer layer S made of Cu having a thickness of 2.4 nm (24A),a fixed layer (pin layer) P and a capping layer C made of titanium (Ti)or tantalum (Ta) having a thickness of 2.5 nm (25A), which are laminatedin this order on the chip 10 a serving as a substrate.

The free layer F is a layer whose magnetization direction varies inaccordance with the direction of the external magnetic field, andcomprises a CoZrNb amorphous magnetic layer 11-1 formed directly on thesubstrate 10 a and having a film thickness of 8 nm (80A), a NiFemagnetic layer 11-2 formed on the CoZrNb amorphous magnetic layer 11-1and having a film thickness of 3.3 nm (33A), and a CoFe layer 11-3formed on the NiFe magnetic layer 11-2 and having a film thickness ofapproximately 1 to 3 nm (10 to 30A). The CoZrNb amorphous magnetic layer11-1 and NiFe magnetic layer 11-2 constitute a soft ferromagneticmaterial thin film layer. The CoFe layer 11-3 prevents Ni of the NiFemagnetic layer 11-2 and Cu 11-4 of the spacer layer S from diffusing.

The fixed layer (pin layer) P is made by superposing a CoFe magneticlayer 11-5 having a film thickness of 2.2 nm (22A), and anantiferromagnetic film 11-6 which is formed of a PtMn alloy including 45to 55 mol % of Pt and has a film thickness of 24 nm (240A). The CoFemagnetic layer 11-5 is in an exchange coupling manner to the magnetizedantiferromagnetic film 11-6. Thus, the direction of magnetization(magnetizing vector) of the CoFe magnetic layer 11-5 is pinned (fixed)in the X-axis negative direction as described above.

The bias magnet films 11 b . . . 11 b gives a bias magnetic field to thefree layer F in the Y-axis negative direction (the direction shown bythe outline arrow in FIGS. 1 and 2) that is the longitudinal directionof the free layer F in order to maintain uniaxial anisotropy of the freelayer F.

The first X-axis GMR element 11 thus configured presents a resistancevalue, which changes in almost proportion to the external magnetic fieldthat changes along the X-axis within a range of −Hc to +Hc, as indicatedby the solid line of FIG. 5, and presents an almost constant resistancevalue to the external magnetic field that changes along the Y-axis, asindicated by the broken line of FIG. 5.

Subsequently, the initializing coils 31 to 34 and 41 to 44 areexplained. The initializing coils 31 to 34 and 41 to 44 are buried inthe lower insulating layer 10 b 2 under the uppermost layer 10 b 1 ofthe insulating layers. The initializing coils 31 to 34 and 41 to 44 arepositioned approximately immediately below each of the GMR elements 11to 14 and 21 to 24, respectively. Each of the initializing coils 31 to34 and 41 to 44 has the same shape to one another, and its relativepositional relationship to the corresponding GMR element immediatelyabove each coil is the same to one another. Each of the initializingcoils 31 to 34 and 41 to 44 applies the initializing magnetic field inthe direction shown by the outline arrow in FIG. 1 to each correspondingGMR element.

The following explanation is made by taking the initializing coil 31 asa representative example. This initializing coil 31 is wound so as tohave an approximately rectangular outer shape viewed in a plane, andcomprises plural initializing magnetic field generating sections 31 a .. . 31 a extending linearly in the direction (X-axis direction)perpendicular to the longitudinal direction of the narrow zonal portions11 a of the first X-axis GMR element 11 at a region immediately belowthe first X-axis GMR element 11 viewed in a plane. Further, one end 31 band the other end 31 c of the initializing coil 31 are connected to apositive polarity and negative polarity of a constant voltage sourcerespectively. When a predetermined condition is established,predetermined current is made to flow through the initializing coil 31,thereby applying the initializing magnetic field in the Y-axis negativedirection to the narrow zonal portion 11 a of the first X-axis GMRelement 11 as shown by the outline arrow in FIG. 1.

Subsequently explained are an X-axis magnetic sensor (a magnetic sensorwith a magnetic field detecting direction which is the X-axis direction)and a Y-axis magnetic sensor (a magnetic sensor with a magnetic fielddetecting direction which is the Y-axis direction) composed respectivelyof the GMR elements 11 to 14 and 21 to 24. As shown by an equivalentcircuit in FIG. 6A, the X-axis magnetic sensor is formed such that thefirst to fourth X-axis GMR elements 11 to 14 are full-bridge-connectedvia a conductor not shown in FIG. 1. In FIG. 6A, each graph shown at theposition adjacent to each of the first to fourth GMR elements 11 to 14indicates a characteristic (change in the resistance value R withrespect to the external magnetic field) of the GMR element adjacent toeach graph. This is also true in FIGS. 7 to 9. Symbols Hx and Hy inthese graphs respectively indicate the external magnetic field whosemagnitude varies along the X-axis and Y-axis.

In this configuration, a connection point between the first X-axis GMRelement 11 and the fourth X-axis GMR element 14 and a connection pointbetween the second X-axis GMR element 12 and the third X-axis GMRelement 13 are respectively connected to the positive polarity and thenegative polarity (ground) of the constant voltage source, whereby apotential of +V (5 (V) in this embodiment) and a potential −V (0 (V) inthis embodiment) are respectively applied thereto. Then, a difference inpotential V_(0X) between a connection point of the first X-axis GMRelement 11 and the third X-axis GMR element 13 and a connection point ofthe fourth X-axis GMR element 14 and the second X-axis GMR element 12are taken out as a sensor output. As a result, the X-axis magneticsensor outputs, as shown in FIG. 6B, an output voltage V_(ox) thatvaries in approximately proportion to the external magnetic field Hxthat changes along the X-axis.

As shown by an equivalent circuit in FIG. 7A, the Y-axis magnetic sensoris formed such that the first to fourth Y-axis GMR elements 21 to 24 arefull-bridge-connected via a conductor not shown in FIG. 1. A connectionpoint between the first Y-axis GMR element 21 and the fourth Y-axis GMRelement 24 and a connection point between the second Y-axis GMR element22 and the third Y-axis GMR element 23 are respectively connected to thepositive polarity and the negative polarity (ground) of the constantvoltage source, whereby a potential of +V (5 (V) in this embodiment) anda potential of −V (0 (V) in this embodiment) are respectively appliedthereto. Then, a difference in potential V_(0y) between a connectionpoint of the first Y-axis GMR element 21 and the third Y-axis GMRelement 23 and a connection point of the fourth Y-axis GMR element 24and the second Y-axis GMR element 22 are taken out as a sensor output.As a result, the Y-axis magnetic sensor outputs, as shown in FIG. 7B, anoutput voltage V_(oy) that varies in approximately proportion to theexternal magnetic field Hy that changes along the Y-axis. The abovedescription is about the configuration of the N-type magnetic sensor 10.

On the other hand, the S-type magnetic sensor 50 includes GMR elements51 to 54 and 61 to 64 and initializing coils 71 to 74 and 81 to 84 asshown in FIG. 1. The S-type magnetic sensor 50 has the substantiallysame structure as that of the magnetic sensor 10 and includes the X-axismagnetic sensor and Y-axis magnetic sensor.

Specifically, as shown by an equivalent circuit in FIG. 8A, the X-axismagnetic sensor is formed such that the first to fourth X-axis GMRelements 51 to 54 are full-bridge-connected via a conductor not shown inFIG. 1. In this configuration, a connection point between the firstX-axis GMR element 51 and the fourth X-axis GMR element 54 and aconnection point between the second X-axis GMR element 52 and the thirdX-axis GMR element 53 are respectively connected to the positivepolarity and the negative polarity (ground) of the constant voltagesource, whereby a potential of +V (5 (V) in this embodiment) and apotential of −V (0 (V) in this embodiment) are respectively appliedthereto. Then, a difference in potential V_(0X) between a connectionpoint of the first X-axis GMR element 51 and the third X-axis GMRelement 53 and a connection point of the fourth X-axis GMR element 54and the second X-axis GMR element 52 are taken out as a sensor output.As a result, the X-axis magnetic sensor outputs, as shown in FIG. 8B, anoutput voltage V_(ox) that varies in approximately proportion to theexternal magnetic field Hx that changes along the X-axis.

Further, as shown by an equivalent circuit in FIG. 9A, the Y-axismagnetic sensor of the magnetic sensor 50 is formed such that the firstto fourth Y-axis GMR elements 61 to 64 are full-bridge-connected via aconductor not shown in FIG. 1. A connection point between the firstY-axis GMR element 61 and the fourth Y-axis GMR element 64 and aconnection point between the second Y-axis GMR element 62 and the thirdY-axis GMR element 63 are respectively connected to the positivepolarity and the negative polarity (ground) of the constant voltagesource, whereby a potential of +V (5 (V) in this embodiment) and apotential −V (0 (V) in this embodiment) are respectively appliedthereto. Then, a difference in potential V_(0y) between a connectionpoint of the first Y-axis GMR element 61 and the third Y-axis GMRelement 63 and a connection point of the fourth Y-axis GMR element 64and the second Y-axis GMR element 62 are taken out as a sensor output.As a result, the Y-axis magnetic sensor outputs, as shown in FIG. 9B, anoutput voltage V_(0y) that varies in approximately proportion to theexternal magnetic field Hy that changes along the Y-axis.

Subsequently explained is a process for manufacturing the magneticsensors 10 and 50 thus configured as described above. Firstly, eachinsulating layer 10 b is laminated on a rectangular quartz glass (wafer)10 a 1, that becomes the substrates 10 a and 50 a later, with theformation of a predetermined wiring or LSI, followed by forming theinitializing coils 31 to 34, 41 to 44, 71 to 74 and 81 to 84 in theinsulating layer 10 b 2, and then, the uppermost insulating layer 10 b 1is formed (see FIGS. 1 to 3).

Then, plural films M composing the GMR elements 11 to 14, 21 to 24, 51to 54 and 61 to 64 are formed like an island. Specifically, said biasfilms 11 b are formed and said films M which will become GMR elements 11to 14, 21 to 24, 51 to 54 and 61 to 64 are formed on the bias film 11 b.This film formation is performed by using a ultra-high vacuum device ina manner of continuous laminating with a precise thickness. The films Mare patterned and thereby plural island-like portions which will becomethe GMR elements are formed. These films M are formed to be arranged ateach position of the GMR elements 11 to 14, 21 to 24, 51 to 54 and 61 to64 shown in FIG. 1 when the quarts glass 10 a 1 is cut along the brokenline in FIG. 10 by a subsequent cutting process to thereby be dividedinto the individual magnetic sensor 10 and 50 shown in FIG. 1.

Subsequently, as shown in FIG. 11 that is a plan view, a rectangularmetal plate 91 is prepared that is provided only with plural squarethrough-holes arranged in a tetragonal lattice (i.e., squarethrough-holes each having sides parallel to the X-axis and Y-axis arearranged along the X-axis and Y-axis so as to be spaced at equalintervals). Each of permanent bar magnets 92 . . . 92 with a shape of arectangular parallelepiped having a square section approximately equalto each through-hole is inserted into each through-hole such that theedge face having a magnetic pole of the permanent bar magnet 92 . . . 92formed thereon becomes parallel to the metal plate 91. At this time, thepermanent bar magnets 92 . . . 92 are arranged such that the polarity ofthe magnetic pole is different from the adjacent polarity by theshortest route in a plane including each edge face of the permanent barmagnets 92 . . . 92. It is to be noted that each of the used permanentbar magnets 92 . . . 92 has magnetic charge whose magnitude isapproximately equal to one another.

Then, as shown in FIG. 12 that represents a section along X-Z plane, aplate 92 is prepared that is made of a transparent quartz glass having athickness of about 0.5 mm and having a rectangular shape approximatelyequal to the metal plate 91. Thereafter, the upper surface (the surfaceopposite to the edge face on which the magnetic pole is formed) of thepermanent bar magnets 92 . . . 92 and the bottom surface of the plate 93are bonded by an adhesive, and then, the metal plate 91 is removed frombelow. At this stage, a magnet array MA is formed by the permanent barmagnets 92 . . . 92 and the plate 93, wherein plural permanent magnets,each having an approximately rectangular parallelepiped shape in whichthe sectional shape perpendicular to one central axis of the rectangularparallelepiped is approximately square, are arranged such that thecenter of gravity of the edge face having approximately square shape ismatched with a lattice point of the tetragonal lattice, and the polarityof the magnetic pole of each permanent magnet thus arranged is differentfrom the polarity of the magnetic pole of the adjacent other permanentmagnet spaced by the shortest route.

FIG. 13 is a perspective view showing a state wherein only fourpermanent bar magnets 92 . . . 92 are taken out. As apparent from thisfigure, there are magnetic fields formed on the edge face (the edge faceon which the magnetic pole is formed) of the permanent bar magnet 92 . .. 92, the magnetic fields from one N-pole directing to the S-polesadjacent to this N-pole by the shortest route and each having adifferent direction at an angle of 90 degrees. In this embodiment, thismagnetic field is used as a magnetic field for magnetizing each biasmagnet film 11 b to 14 b, 21 b to 24 b, 51 b to 54 b and 61 b to 64 b ofeach GMR element 11 to 14, 21 to 24, 51 to 54 and 61 to 64 and as amagnetic field for fixing the direction of magnetization in each fixedlayer P (pinned layer in the fixed layer P).

Specifically, as shown in FIG. 14, the quartz glass 10 a 1 on which thefilm M which will become the GMR element is formed is firstly arrangedsuch that the face having the film M which will become the GMR elementformed thereon comes in contact with the upper surface of the plate 93,and then, the plate 93 and the quartz glass 10 a 1 are fixed to eachother by a cramp C. At this time, as shown in FIG. 15 that is a planview for enlarging the section that becomes later the magnetic sensors10 and 50 by paying attention to the section corresponding to two of themagnetic sensors 10 and 50, the quartz glass 10 a 1 and the magnet arrayMA are relatively arranged such that each cross-point CP of the cuttingplane line CL of the quartz glass 10 a 1 that becomes each side of themagnetic sensors 10 and 50 is matched with the respective center ofgravity of the permanent bar magnets 92 . . . 92. Accordingly, as shownby arrows in FIG. 15, a magnetic field is applied to each film M whichwill become the GMR element in the longitudinal direction of the narrowzonal portion of each film M in the state wherein the quartz glass 10 a1 is placed on the upper surface of the plate 93.

The present embodiment utilizes this magnetic field for magnetizing thebias magnet films 11 b to 14 b, 21 b to 24 b, 51 b to 54 b and 61 b to64 b as well as for matching the direction of magnetization in eachmagnetic domain in the free layer F with the direction in the initialstate. That is, magnetization in each magnetic domain in the free layerF is initialized.

Subsequently, the relative relationship between the quartz glass 10 a 1having the film M which will become the GMR element formed thereon andthe magnet array MA (plate 93) is changed as shown in a plan view ofFIG. 16, whereby the surface on which the film M which will become theGMR element is formed is arranged to be brought into contact with theupper surface of the plate 93. At this time, the quartz glass 10 a 1 andthe magnet array MA are relatively arranged such that each cross-pointof the cutting plane line CL of the quartz glass 10 a 1 that becomeseach side of the magnetic sensors 10 and 50 is matched with therespective center of gravity of the four adjacent permanent bar magnets92 . . . 92. Accordingly, as shown by arrows in FIG. 16, a magneticfield is applied to each film M which will become the GMR element in thedirection perpendicular to the longitudinal direction of the narrowzonal portion of each film M in the state wherein the quartz glass 10 a1 is placed on the upper surface of the plate 93.

The present embodiment utilizes this magnetic field for performing aheat treatment (annealing for ordering) to fix the direction ofmagnetization in the fixed layer P (pinned layer of the fixed layer P).Specifically, the plate 93 and the quartz glass 10 a 1 are fixed to eachother by the cramp C with the state shown in FIG. 16, then, theresultant is heated in a vacuum to 250 to 280° C. and left for aboutfour hours in this state.

Thereafter, the quartz glass 10 a 1 is removed to form a wiring or thelike for connecting each film M, and finally, the quartz glass 10 a 1 iscut along the broken line (or the cutting line CL) shown in FIG. 10 etc.As described above, a great number of magnetic sensors 10 and 50 shownin FIG. 1 are simultaneously produced.

As described above, a magnetic sensor according to the embodiment of thepresent invention has bias magnet films 11 b . . . 11 b provided at bothends of the free layer F in the longitudinal direction for producing inthe free layer a bias magnetic field in a predetermined direction (inthe longitudinal direction of the free layer), whereby the direction ofmagnetization in each magnetic domain in the free layer can stably bemaintained in the predetermined direction when an external magneticfield is not present.

Further, the initializing coils 31 to 34 and 41 to 44 are energizedunder a predetermined condition to thereby generate an initializingmagnetic field for returning the direction of magnetization in eachmagnetic domain in the free layer to the direction (i.e., thelongitudinal direction of the free layer) same as the direction of thebias magnetic field by the bias magnet films, whereby the direction ofmagnetization in each magnetic domain in the free layer can assuredly bereturned to the initial state even if the direction of magnetization isdisturbed by applying a strong magnetic field to the free layer. As aresult, a hysteresis that occurs when the external magnetic field is inthe vicinity of “0” with respect to the change of the external magneticfield can be maintained small of the magnetic sensors 10 and 50. Thus,the magnetic sensor is capable of detecting a minute magnetic field withhigh precision over a long period.

Further, according to the production process of the magnetic sensoraccording to the embodiment of the present invention, there is prepareda magnet array MA that is configured such that plural permanent magnetsare arranged at a lattice point of a tetragonal lattice and the polarityof the magnetic pole of each permanent magnet is different from thepolarity of the other adjacent magnetic pole spaced by the shortestroute. Therefore, the direction of magnetization in each magnetic domainin the free layer is initialized and the bias magnet films aremagnetized, and further, a pinning is performed by pinning the directionof magnetization in the magnetic layer that becomes a pinned layer.Accordingly, plural GMR elements having different magnetic fielddetecting directions (perpendicular to each other) can easily andefficiently be formed on a single chip, thereby being capable ofmanufacturing with low cost a magnetic sensor of a single chip which iscapable of detecting at least respective magnetic fields whose magnitudeis changed in the directions perpendicular to each other.

It should be noted that, in the above embodiment, the films M for GMRfilms (films M which will be the GMR elements) are formed after the biasfilms (films for magnets) are patterned, and the films M for GMR filmsare annealed for ordering after the GMR films are patterned. However,the annealing process for ordering can be performed before the films Mfor GMR films are patterned. Further, the bias films can be formed afterthe films M for GMR films are formed.

Next, another embodiment of a magnetic sensor (second embodiment) inaccordance with the present invention will be described. This magneticsensor is also classified into N-type shown in FIG. 21 which is a planview of the N-type sensor and S-type shown in FIG. 22 which is a planview of the S-type sensor. The N-type magnetic sensor 110 and the S-typemagnetic sensor 150 have substantially the same shape and sameconfiguration except that a direction of fixed magnetization in a pinnedlayer shown by black-solid arrows in FIGS. 21 and 22 and a direction ofmagnetization in an initial state in a free layer shown by outlinearrows in FIGS. 21 and 22 are different from each other. Note that,initializing coils are omitted in FIGS. 21 and 22.

The N-type magnetic sensor 110 has the same structure as the N-typemagnetic sensor 10 except the position of the GMR elements and theinitializing coils. The N-type magnetic sensor 110 comprises a singlechip 110 a which is the same as the single chip 10 a, insulating layerswhich is the same as the insulating layers 10 b, a total of eight GMRelements 111 to 114, 121 to 124 formed on the uppermost layer of theinsulating layers and a total of eight initializing coils (coils forinitializing). A relative positional relationship between the GMRelements 111 to 114, 121 to 124 and the eight initializing coils is thesame as that between the GMR elements 11 to 14, 21 to 24 and theinitializing coils 31 to 34, 41 to 44. The GMR elements 111 to 114 forman X-axis magnetic sensor by being full-bridge-connected similarly tothe GMR elements 11 to 14. The GMR elements 121 to 124 form an Y-axismagnetic sensor by being full-bridge-connected similarly to the GMRelements 21 to 24.

The first X-axis GMR element 111 is formed at an almost central portionin the Y-axis direction of the chip 110 a and in the vicinity of an endportion of the X-axis negative direction. The second X-axis GMR element112 is formed at an almost central portion in the Y-axis direction ofthe chip 110 a and at a portion spaced by a predetermined short distancein the X-axis positive direction from the first X-axis GMR element 111.The third X-axis GMR element 113 is formed at an almost central portionin the Y-axis direction of the chip 110 a and in the vicinity of an endportion of the X-axis positive direction. The fourth X-axis GMR element114 is formed at an almost central portion in the Y-axis direction ofthe chip 110 a and at a portion spaced by a predetermined short distancein the X-axis negative direction from the third X-axis GMR element 113.An each of longitudinal directions of the first to fourth X-axis GMRelements 111 to 114 is parallel to the Y-axis direction.

The first Y-axis GMR element 121 is formed at an almost central portionin the X-axis direction of the chip 110 a and in the vicinity of an endportion of the Y-axis positive direction. The second Y-axis GMR element122 is formed at an almost central portion in the X-axis direction ofthe chip 110 a and at a portion spaced by a predetermined short distancein the Y-axis negative direction from the first Y-axis GMR element 121.The third Y-axis GMR element 123 is formed at an almost central portionin the X-axis direction of the chip 110 a and in the vicinity of an endportion of the Y-axis negative direction. The fourth Y-axis GMR element124 is formed at an almost central portion in the X-axis direction ofthe chip 110 a and at a portion spaced by a predetermined short distancein the Y-axis positive direction from the third Y-axis GMR element 123.An each of longitudinal directions of the first to fourth Y-axis GMRelements 121 to 124 is parallel to the X-axis direction.

The S-type magnetic sensor 150 has the same structure as the S-typemagnetic sensor 50 except the position of the GMR elements and theinitializing coils. The magnetic sensor 150 comprises a single chip 150a which is the same as the single chip 50 a, insulating layers which isthe same as the insulating layers 10 b, a total of eight GMR elements151 to 154, 161 to 164 formed on the uppermost layer of the insulatinglayers and a total of eight initializing coils (coils for initializing).A relative positional relationship between the GMR elements 151 to 154,161 to 164 and the eight initializing coils is the same as that betweenthe GMR elements 51 to 54, 61 to 64 and the initializing coils 71 to 74,81 to 84. The GMR elements 151 to 154 form an X-axis magnetic sensor bybeing full-bridge-connected similarly to the GMR elements 51 to 54. TheGMR elements 161 to 164 form an Y-axis magnetic sensor by beingfull-bridge-connected similarly to the GMR elements 61 to 64.

A positional relationship between the first to fourth X-axis GMRelements 151 to 154 and the substrate 150 a is the same as that betweenthe first to fourth X-axis GMR elements 111 to 114 and the substrate 110a. An each of longitudinal directions of the first to fourth GMRelements 151 to 154 is parallel to the Y-axis direction. A positionalrelationship between the first to fourth Y-axis GMR elements 161 to 164and the substrate 150 a is the same as that between the first to fourthY-axis GMR elements 121 to 124 and the substrate 110 a. An each oflongitudinal directions of the first to fourth GMR elements 161 to 164is parallel to the X-axis direction.

Subsequently explained is a process for manufacturing the magneticsensors 110 and 150 thus configured as described above. In this process,the magnet array MA described above and a magnet array MB which isdifferent from the magnet array MA are used.

Firstly, the magnet array MA is prepared by the process mentioned aboveand the magnet array MB is prepared by the following process below.Prior to the process to make the magnet array MB, each of parts thatconstitute magnet array MB is explained. The magnet array MB comprises ayoke (yoke plate) 200, a substrate for the array 210 and pluralpermanent magnets (permanent bar magnets) 230.

The yoke 200 is shown in FIGS. 23, 24 and 25. FIG. 23 is a fragmentaryplan view of the yoke 200, FIG. 24 is an enlarged plan view of FIG. 23and FIG. 25 is a sectional view of the yoke shown in FIG. 24 cut by aplane along a line 2-2 in FIG. 24. This yoke 200 is a thin plate formedof magnetic material which has larger permeability than air (e.g., 42alloy . . . Fe-42Ni alloy and the like). Preferably, yoke 200 can beformed of high saturation-high permeability material such as permalloyor silicon steel (silicon sheet). The planar shape of the yoke isrectangle. The plate thickness of the yoke 200 is 0.15 mm in thisexample. The yoke 200 has plural thorough holes 201. The through hole201 has an approximately square shape viewed in a plane. The pluralthrough holes 201 are arranged in a tetragonal lattice. Specifically,the through holes 201 are disposed such that each center of gravity ofthe through holes 201 is matched with a lattice point SP of thetetragonal lattice shown in FIG. 24. As viewed in a plane, a certainside of sides forming the through hole 201 is parallel to a certain sideof sides forming the adjacent through hole 201. In other words, acertain side of sides forming the through hole 201 and a certain side ofsides forming other through hole 201 located on the same row (or column)of the tetragonal lattice are on (in) a same straight line.

Each of the through holes 201, as shown in FIG. 26 showing a planarshape of the through hole 201, has a shape composed of a square portion201 a and margin portions (circle arc portions or R portions) 201 bviewed in a plane. A shape of the square portion 201 a is a square. Themargin portion 201 b swells outwardly from the square at each of cornersof the square portion 201 a. Specifically, an outer shape (outline) ofthe margin portion 201 b is a circle arc whose center PR is on adiagonal line CR of the square portion 201 a.

Through openings 202 serving as air gaps are formed between the throughhole 201 and the other adjacent through hole 201 spaced by the shortestroute from the former through hole 201 (i.e., between through holes 201,201 that are adjacent each other with a shortest distance). A shape ofthe through opening 202 is approximately a rectangle in viewed in aplane. A longer side of the through opening 202 is parallel to a side ofthe square portion 201 b of the through hole 201 next to the samethrough opening 202. Length of the longer side of the through opening202 is approximately the same as or is slightly shorter than length ofthe side of the square portion 201 a. Length of the shorter side of thethrough opening 202 is longer than length of the longer side (side inthe longitudinal direction) of each of the films M which will become GMRelements 111 to 114, 121 to 124, 151 to 154 and 161 to 164.

The yoke 200 has openings (openings for controlling magnetic flux) 203.The opening 203, viewed in a plane, is formed at a region surrounding acenter of gravity SQ of a square drawn by lines connecting the latticepoints of the tetragonal lattice. One of the openings 203 has a shape ofa circle whose center is on the center of gravity SQ viewed in a plane.

The substrate for the array 210, shown in FIGS. 27 and 28, is asubstrate made by processing a thin plate 210 a, shown in FIG. 29,formed of magnetic material (e.g., permalloy). The substrate for thearray 210 has almost the same shape as the yoke 200 viewed in a plane.The substrate for the array 210 includes plural concavities (ditches)210 b. Plural concavities 210 b are formed at the same positions (samelocations) as the through holes 201 of the yoke 200. A shape of theconcavity 210 b is almost the same as the shape of the square portion201 a of the through hole 201.

The permanent bar magnets 230 has a shape of a rectangularparallelepiped shape (see. FIG. 31.). The permanent bar magnet 230 has asectional shape, perpendicular to one relatively longer central axis ofthe rectangular parallelepiped, which is an approximately square shapeapproximately same as the shape of the through hole 201 (and theconcavity 210 b). Poles of the permanent bar magnet 230 are formed atboth edge faces each of which has the square shape. Magnitude of each ofmagnetic charges of the plural permanent bar magnets 230 isapproximately equal to one another.

Subsequently explained is a process for manufacturing the magnet arrayMB. Firstly, a thin plate which will become the yoke 200 is prepared.The through holes 201, the through openings 202 and the openings 203 areformed in the thin plate by etching. Next, the concavities 210 b areformed on the thin plate 210 a which will become the substrate for thearray 210 by etching (by half-etching).

Next, square column-like spacers (bar) 220 are disposed on the substratefor the array 210, as shown in FIG. 30 which is a perspective view andin FIG. 31 which is a sectional view. The spacers 220 are placed betweenone row constituted by the plural concavities 210 b and the other row,constituted by the plural concavities 210 b, which is next to and isparallel to the former row. When the spacers 220 are arranged in thismanner, length of the spacer 220 along the Z-axis direction is shorterthan length between both edge faces having magnetic poles of thepermanent bar magnet 230. Note that the margin portions 201 b areomitted in FIG. 30.

Subsequently, the yoke 200 is placed (disposed or arranged) on thespacers 220. At this time, the yoke 200 is arranged in such a mannerthat the through holes 201 (the square portions 201 a) of the yoke 200and the concavities 210 b of the substrate for the array 210 coincide ina plan view. In other words, in a state where the yoke 200 is disposedon the spacers 220, each of the concavities 210 b coincides with eachone of the through holes 201 in a Z-axis direction. Note that a mark fordetermining position of them (i.e., an alignment mark) may be formed onthe yoke 200 and the substrate for the array 210.

Next, each of the plural permanent bar magnets 230 is inserted into eachof the plural through holes 201. At the time of the insertion of thepermanent bar magnets 230, one of the edge faces having magnetic polesof the permanent bar magnets 230 is made to be in abutment (contact)with each of upper surfaces of the concavities 210 b of the substratefor the array 210. As a result, the other edge faces having magneticpoles of the permanent bar magnets 230 (this face is also simplyreferred to as “upper surface” of the magnet 230 hereinafter) is placed(disposed) in a same plane (on a single plane). Also, at this time, inthe plane where the upper surfaces of the magnet 230 is disposed, apolarity of a magnet pole of each permanent magnet 230 is different from(opposite to) a polarity of the other adjacent magnet pole spaced by theshortest route (i.e., shortest distance). Accordingly, the permanent barmagnet 230 is arranged as shown in FIG. 23. In this stage, a movement ofthe permanent bar magnets 230 in a side direction (in a transversedirection) is prohibited because the magnets 230 are inserted into boththe through holes 201 of the yoke 200 and the concavities 210 b.

Next, the yoke 200 is lifted upwardly (in the Z-axis positive direction)by utilizing the openings 203 of the yoke 200. More specifically, two ofthe openings 203 are grasped with tweezers and the yoke 200 is lifted bythe tweezers. This operation is repeated for the other openings 203 andthe whole yoke is gradually lifted upward. At this time, as shown inFIG. 33, height of the yoke 200 (distance between the yoke 200 and thesubstrate for the array 210) is adjusted in such a manner that the planeformed by the upper surfaces of the permanent bar magnets 230 (i.e., allthe other edge faces having magnetic poles of the permanent bar magnets230) is placed between an upper surface 200 up of the yoke 200 and alower surface 200 dn of the yoke 200. In other words, the yoke 200 islifted upwardly such that the upper surface of the permanent bar magnet230 is made to be within plate thickness of the yoke 200. It should benoted that a plane formed by the upper surface 200 up of the yoke 200coincides with a plane formed by the upper surfaces of the permanent barmagnets 230. Then, the spacers are taken out and the yoke 200 is fixedto the substrate for the array 210. The magnet array MB is thuscompleted.

FIG. 34 is a perspective view showing a state wherein only fourpermanent bar magnets 230 . . . 230 are taken out. As is apparent fromthis figure, there are provided magnetic fields from one N-poledirecting to the S-poles adjacent to this N-pole by the shortest routeand each having a different direction at an angle of 90 degrees, abovethe upper surfaces (edge faces having the pole) of the permanent barmagnets 230 . . . 230. In this embodiment, this magnetic field given bythe magnet array MB is used as a magnetic field for magnetizing eachbias magnet film of each GMR element 111 to 114, 121 to 124, 151 to 154and 161 to 164.

This magnet array MB has through openings 202 serving as air gaps formedbetween two of (upper surfaces of) the permanent bar magnets 230 thatare spaced by the shortest route and next to each other. With thisconfiguration, as shown in FIG. 35, magnetic flux concentrates both inthe through openings 202 and in a space close to the through openings202. In other words, the magnet array MB can provide a narrow spacelocal region with a magnetic field whose magnitude is great and whosedirection is stably constant.

FIGS. 36 and 37 show states of magnetic flux generated by the magnetarray MB and the magnet array MA by arrows, respectively. As understoodby comparing one of the figures with the other figure, the magnet arrayMB has not only above mentioned through openings 202 but also openings203, and therefore, it can make the magnetic field formed between boththe permanent bar magnets that are next to each other and are spaced bythe shortest route more linear and can provide locally the magneticfield which is more stable and whose magnitude is greater than themagnetic field provided by the magnet array MA.

With these steps mentioned above, the magnet array MA and the magnetarray MB are prepared. Therefore, the concrete process (method) formanufacturing (producing) the magnetic sensors 110 and 150 is explained,hereinafter.

Firstly, a substrate (a quartz glass that will become a substrate 110 a1 described later with reference to FIG. 39, a wafer) is prepared onwhich films M, which will become the GMR elements 111 to 114, 121 to124, 151 to 154, 161 to 164, are formed. This substrate is formed in amanner similar to the substrate 10 a 1 shown in FIG. 10. These films Mare arranged in such a manner that, when this substrate is cut in thecutting process which will be carried out later, individual magneticsensors 110 and 150 shown in FIGS. 21 and 22 are obtained.

Next, the above mentioned substrate on which films M which will becomethe GMR elements are formed and the magnet array MA (the plate 93) arearranged as shown in FIG. 38, and relative positional relationshipbetween them is fixed. At this time, they are disposed in such a mannerthat a surface on which the films M which will become the GMR elementsare formed is made to come in contact with (be in abutment with) anupper surface of the plate 93 (see. FIG. 14.). Further, the substrateand the magnet array MA are relatively arranged in such a manner thateach cross-point CP of the cutting plane line CL of the substrate thatbecomes each side of the magnetic sensors 110 and 150 is matched withthe respective center of gravity of the four adjacent permanent barmagnets 92 . . . 92. As a result, a magnetic field is applied to eachfilm M which will become the GMR element in the direction perpendicularto the longitudinal direction of the narrow zonal portion of each film Min the state wherein the substrate is placed on the upper surface of themagnet array MA, as shown by arrows in FIG. 38.

This second embodiment utilizes this magnetic field for performing aheat treatment to fix the direction of magnetization in the fixed layerP (pinned layer of the fixed layer P). Specifically, the plate 93 andthe substrate are fixed to each other by the cramp C (see. FIG. 14) withthe state shown in FIG. 38, then, the resultant is heated in a vacuum to250 to 280° C. and left for about four hours in this state (i.e., theannealing for ordering is performed).

Next, as shown in FIG. 39, the substrate 110 a 1 on which the films Mwhich will become the GMR elements are formed is arranged in such amanner that the plane on which the films M which will become the GMRelements are formed comes in contact with (is in abutment with) theupper surface 200 up of the yoke 200 of the magnet array MB. At thistime, as shown in FIG. 40 which is a fragmentary enlarged plan view, thesubstrate and the magnet array MB are relatively arranged in such amanner that each cross-point CP of the cutting plane line CL of thesubstrate 110 a 1 that becomes each side of the magnetic sensors 110 and150 is matched with the respective center of gravity of the eachpermanent bar magnet 230 . . . 230. At this time, the films M which willbe the GMR elements is disposed inside of the through openings 202 ofthe yoke 200, in viewed in a plane. Accordingly, as shown by arrows inFIG. 40, a magnetic field is applied to each film M which will becomethe GMR element in the longitudinal direction of the narrow zonalportion of each film M in the state wherein the substrate 110 a 1 isplaced on the upper surface 200 up of the yoke 200.

This second embodiment utilizes this magnetic field for magnetizing thebias magnet films as well as for matching the direction of magnetizationin each magnetic domain in the free layer F with the direction in theinitial state.

Thereafter, the substrate 110 a 1 is removed to form a wiring or thelike for connecting each film M, and finally, the substrate 110 a 1 iscut along the broken line shown in FIGS. 38 and 40. As described above,a great number of monolithic (single chip) magnetic sensors 110 shown inFIG. 21 and monolithic (single chip) magnetic sensors 150 shown in FIG.22 are simultaneously produced.

As explained above, in the second embodiment, the strong magnetic fieldis provided at local space by utilizing the magnet array MB, and themagnetic field thus provided is used to magnetize the bias magnet filmsof the GMR elements. The magnet array MB comprises the yoke havingthrough openings 202 serving as air gaps. Therefore, the magnet array MBcan provide a space close to the through openings 202 with a magneticfield whose magnitude is great and which is stably constant.Accordingly, even if the magnetic material having a high coersive forceis adopted to the bias magnetic film, the bias magnetic film can beassuredly magnetized. As a result, a high reliable magnetic sensor 110and 150 can be provided in which the direction of magnetization in thefree layer is stably returned to the initial-state direction even afterthe strong disturbance (e.g., a magnetic field whose magnitude isrelatively large) is added to the magnetic sensor.

In addition, the yoke 200 has the openings 203 formed at regions wherethe magnetic fields are unstable because of crossing (or collision) ofmagnetic flux lines stemming from the poles. As a result, since thedirection of the magnetic flux lines become stable, the magnetic fieldin the region in the neighborhood of the through opening 202 becomesmore stable. Further, the openings 203 are used to adjust the distancebetween the substrate for the array 210 of the magnet array MB and theyoke 200 (i.e., the height of the yoke 200). Therefore, since it ispossible to adjust the height of the yoke easily and desirably, anoptimum magnetic field can be provided for a region where the biasmagnetic film of the GMR element is disposed to be magnetized.

Moreover, the through hole 201 of the yoke 200 of the magnet array MBhas the shape which is not a square shape but which includes the marginportions 201 b swelling outwardly from the square at each of corners ofthe square. Therefore, when forming the through hole 201 by etching,even if the corner of the through hole is not completely etched asdesigned, the permanent bar magnet 230 can be assuredly inserted intothe through hole 201. It should be noted that this type of marginportion may preferably be formed at corners of the concavities 210 b.

The present invention is not limited to the above-mentioned embodiment,but various modifications can be applied within the scope of the presentinvention. For example, as shown in FIG. 20 representing a first X-axisGMR element 301 taking as a representative example, narrow zonalportions 301 a may be separated at the upper portion of the bias magnetfilms 301 b . . . 301 b disposed below both ends thereof. Further, aninitializing coil 302 may be a double spiral type coil wherein a spiralcoil 302-1 having a center point P1 and a spiral coil 302-2 having acenter point P2 are connected to each other. In this case, the firstX-axis GMR element 301 is arranged between the center point P1 and thecenter point P2, resulting in that currents parallel to each other flowin the same direction (in a direction perpendicular to the longitudinaldirection of the narrow zonal portions 301 a) through each conductorsection of the initializing coil 302 passing below the first X-axis GMRelement 301, thereby generating the initializing magnetic field.Moreover, the initializing coil may be a multi-layered coil or may be atoroidal coil. Further, a testing coil that generates a testing magneticfield, in the direction perpendicular to the initializing magnetic fieldgenerated by the initializing coil, for checking a function of each GMRelement may also be disposed in the insulating layer above or below(Z-axis direction) the initializing coil.

1. A magnetic sensor comprising: a plurality of full-bridge-connectedgiant magnetoresistive effect elements, each giant magnetoresistiveeffect element having a spin valve film including a pinned layer, aconductive spacer layer, and a free layer, wherein the spin valve filmshave narrow zonal portions each of which extends in the longitudinaldirection comprising: bias magnet films provided at both ends of thefree layer in the longitudinal direction for producing in the free layera bias magnetic field in the longitudinal direction of the free layer,whereby the direction of magnetization in each magnet domain in the freelayer can stably be maintained in the predetermined direction when anexternal magnetic field is not present, and initializing coils beingenergized under a predetermined condition to thereby generate aninitializing magnetic field for returning the direction of magnetizationin each magnetic domain in the free layer to the longitudinal directionof the free layer, whereby the direction of magnetization in eachmagnetic domain in the free layer can assuredly be returned to theinitial state even if the direction of magnetization is disturbed byapplying a strong magnetic field to the free layer.
 2. A magnetic sensorcomprising: a plurality of full-bridge-connected giant magnetoresistiveeffect elements, each giant magnetoresistive effect element having aspin valve film including a pinned layer, a conductive spacer layer, anda free layer, wherein free layer comprises: a bias magnet film composedof a permanent magnet for producing a bias magnetic field in the freelayer in a predetermined direction so that the direction ofmagnetization in each magnetic domain in the free layer can bemaintained in the predetermined initial state direction; and aninitializing coil that is provided in the vicinity of the free layer andapplies to the free layer an initializing magnetic field in thedirection same as the direction of the bias magnetic field by beingenergized under a predetermined condition so that the direction ofmagnetization in each magnetic domain in the free layer can assuredly bereturned to initial state direction even if the direction ofmagnetization is disturbed by applying a strong magnetic field to thefree layer.